linux-kernel - Re: [PATCH 0/3] Allow specifying an S2RAM sleep on pre-SYSTEM

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Message-ID: <20241113165329590-0800.eberman@hu-eberman-lv.qualcomm.com>
Date: Wed, 13 Nov 2024 17:10:24 -0800
From: Elliot Berman <quic_eberman@...cinc.com>
To: Konrad Dybcio <konradybcio@...nel.org>
CC: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Lorenzo Pieralisi
	<lpieralisi@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Marijn Suijten
	<marijn.suijten@...ainline.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        "Bjorn Andersson" <bjorn.andersson@....qualcomm.com>,
        Konrad Dybcio
	<konrad.dybcio@....qualcomm.com>,
        Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH 0/3] Allow specifying an S2RAM sleep on
 pre-SYSTEM_SUSPEND PSCI impls

On Mon, Oct 28, 2024 at 03:22:56PM +0100, Konrad Dybcio wrote:
> Certain firmwares expose exactly what PSCI_SYSTEM_SUSPEND does through
> CPU_SUSPEND instead. Inform Linux about that.
> Please see the commit messages for a more detailed explanation.
> 
> This is effectively a more educated follow-up to [1].
> 
> The ultimate goal is to stop making Linux think that certain states
> only concern cores/clusters, and consequently setting
> pm_set_suspend/resume_via_firmware(), so that client drivers (such as
> NVMe, see related discussion over at [2]) can make informed decisions
> about assuming the power state of the device they govern.
> 
> If this series gets green light, I'll push a follow-up one that wires
> up said sleep state on Qualcomm SoCs across the board.
> 
> [1] https://lore.kernel.org/linux-arm-kernel/20231227-topic-psci_fw_sus-v1-0-6910add70bf3@linaro.org/
> [2] https://lore.kernel.org/linux-nvme/20241024-topic-nvmequirk-v1-1-51249999d409@oss.qualcomm.com/
> 

I got a bit confused, but I think I might've pieced it together. Konrad
wants to support s2ram (not clear why) on Qualcomm SoCs from 2015-2023.
On these SoCs, PSCI_SYSTEM_SUSPEND (s2ram) isn't supported but doing
s2idle gets you the same effect. You'd like s2ram to work, so you
provide a way to replace the PSCI_SYSTEM_SUSPEND param with
(effectively) the CPU_SUSPEND command. If this is the wrong
understanding, please correct me.

Could patch 2 be sent separately? I think it seems fine without the
rest of the series.

I'm not sure why you'd like to support s2ram. Is it *only* that you'd
like to be able to set pm_set_supend/resume_via_firmware()? I hope this
doesn't sound silly: what if you register a platform_s2idle_ops for the
relevant SoCs which calls pm_set_suspend/resume_via_firwmare()?

- Elliot